Distinguishing between general nas level congestion and s-nssai related congestion control

ABSTRACT

A RAN node includes means for receiving a N2 message containing a list of S-NSSAI of the congested network slice from an AMF and means for sending the list of S-NSSAI and a wait timer for each S-NSSAI in the list in first AN signaling message to an UE when receiving, from the UE, second signaling message containing the list of S-NSSAI to establish an AN signaling connection, the S-NSSAI being indicated in the N2 message as congested by the AMF.

TECHNICAL FIELD

This invention is related to a procedure of handling network congestion.More specifically this invention is related to a procedure whichindicates different type of network congestion to the UE by the network.

BACKGROUND ART

Non patent literature 1 (TS23.501 V15.0.0) shows 5G System Architecture(see FIG. 10) and some overload/congestion control methods. One exampleof the control methods is AMF Overload Control as below.

Under unusual circumstances, if AMF has reached overload situation, theAMF activates NAS level congestion control as specified in Clause 5.19.7of the Non patent literature 1 and AMF restricts the load that the ANnode(s) are generating, if the AN is configured to support overloadcontrol. N2 overload control can be achieved by the AMF invoking the N2overload procedure (see TS 38.300 and TS 38.413) to all or to aproportion of the AN nodes with which the AMF has N2 connections. TheAMF may include the S-NSSAI(s) in N2 overload control message sent to ANnode(s) to indicate the congestion of the Network Slice(s) at the CNpart. To reflect the amount of load that the AMF wishes to reduce, theAMF can adjust the proportion of AN nodes which are sent NGAP OVERLOADSTART message, and the content of the overload start procedure.

The AMF should select the 5G-AN node(s) to which it triggers overloadstart procedure at random to avoid that multiple AMFs in an AMF Setrequest reduction of load from the same subset of 5G-AN node(s).

An AN node supports rejecting of AN signalling connection establishmentsfor certain UEs as specified in TS 38.331. Additionally, an AN nodeprovides support for the barring of UEs as described in TS 22.261. Thesemechanisms are further specified in TS 38.331.

Using the overload start procedure, the AMF can request the AN node to:

-   -   reject AN signaling connection (RRC connection over 3GPP access        or UE-N3IWF connection over N3GPP access) requests that are for        non-emergency and non-high priority mobile originated services;        or    -   reject new AN signaling connection requests for uplink NAS        signalling transmission to that AMF;    -   release AN signalling connection for uplink NAS signalling        transmission where the Requested NSSAI at AS layer only includes        the indicated S-NSSAI(s).    -   only permit AN signaling connection requests for emergency        sessions and mobile terminated services for that AMF; or    -   only permit AN signaling connection requests for high priority        sessions and mobile terminated services tbr that AMF;

The AN signaling connection requests listed in this clause also includethe request from UE in RRC-Inactive state.

The AMF can provide percentage value that indicates how much amount ofsignalling traffic to be rejected in the overload start message, and theAN node may consider this value for congestion control.

When rejecting an AN signaling connection request for overload reasonsthe AN indicates to the UE an appropriate wait timer value that limitsfurther AN signaling connection requests for a while.

During an overload situation, the AMF should attempt to maintain supportfor emergency services and for MPS.

When the AMF is recovering, the AMF can either:

-   -   trigger overload start procedure with new percentage value that        permit more signalling traffic to be carried, or    -   the AMF trigger overload stop procedure. to some or all of the        5G-AN node(s).

CITATION LIST Non Patent Literature

NPL 1: TS23.501 V15.0.0 (2017-12)

SUMMARY OF INVENTION Technical Problem

General Problem Statement

According to the description of the AMF Overload Control in thenon-patent document 1, the AMF may include the S-NSSAI(s) in N2 overloadcontrol message sent to AN node(s). However, in the current procedure,the UE cannot perform an appropriate behaviour regarding the congestionas information which is sent from the AN node is insufficient.

This invention solves following five issues which are related to generalNAS level congestion control mechanism and network slice congestioncontrol mechanism.

Problem Statement 1:

No information is sent with wait timer to the UE to identify if waittimer is related to General NAS level congestion or a network slicecongestion.

Under general overload condition the network applies General NAScongestion control mechanism and sends a message to NG-RAN instructingNG-RAN to reject a request to establish an AN signalling connection.Following this, the NG-RAN rejects AN Signalling connection and sendswait timer in an AN signalling message.

Under a network slice overload condition, the AMF sends a messageincluding network slice id (S-NSSAI(s)) of the congested network sliceto the NG-RAN to reject the AN signalling connection. The NG RAN willreject the AN signalling connection and send wait time to the UE in a ANsignalling connection.

So a wait timer is sent to the UE under two situations when a AMFapplies General NAS level congestion control and a network slice relatedcongestion control. The UE doesn't know whether the wait timer isrelated to a network slice congestion or a general NAS level congestion.Therefore, the UE behaviour becomes non deterministic when it receives await time without an indication identifying whether the wait timer isrelated to general NAS level congestion timer or a network slicecongestion.

Problem Statement 2:

Network Slice Identifier of the congested network slice with wait timeris not being sent to the UE.

When the NG-RAN receives a message containing network slice identifierof the congested network slice to start the overload control procedure,then NG-RAN is releasing or rejecting the AN signalling connectionwithout sending the wait time and a network slice identifier of thecongested network. The UE may again initiate procedure (NAS or AS)related to congested network slice and may again congest the network(AMF/SMF/NG-RAN).

Problem Statement 3:

No mechanism is defined to handle a scenario at NG-RAN for a UE whensome network slice related to the UE are congested and some networkslice related to the UE are not congested.

The NG-RAN receives a message (e.g. NGAP OVERLOAD START) containing anetwork slice identifier of the congested network slice from the AMF tostart congestion control related to the network slice. The UE has a PDUsession(s) established related to the network slice and a PDU session(s)related to other network slice. In this scenario the NG-RAN behaviourregarding the UE is not clear or non-deterministic. It is not clearwhether the NG-RAN will release all AN connection or only release theresources related to the congested network slice only.

Problem Statement 4:

When a AN connection is established during the service requestprocedure, the S-NSSAI for which the service request procedure isinitiated is not included in the AN signalling message. Since a ANsignalling Request message doesn't contain requested NSSAI during ANsignalling establishment procedure therefore the RAN cannot perform RANoverload control procedure related to a congested network slice. If alot of UE is initiating service request procedure to establish a PDUsession then AN cannot reject AN connection establishment and send themessage to AMF or SMF then the AMF/SMF gets further congested. This maylead to severe network failure.

Problem Statement 5:

When a UE is establishing a AN signalling connection related to aS-NSSAI to N3IWF for a non-3GPP access, then no procedure is defined tosend a congested S-NSSAI and corresponding wait time.

Solution to Problem

A Next Generation Radio Access Network (NG-RAN) node according to afirst exemplary aspect of the present disclosure includes an NGinterface connected with an Access-mobility Management Function (AMF), atransceiver configured to communicate with a User Equipment (UE), aprocessor configured to receive, from the AMF via the NG interface, NGAPOVERLOAD START message including a first Single Network SlicingSelection Assistance Information (S-NSSAI) list that includes one ormore S-NSSAIs indicating one or more congested network slicesrespectively receive, from the UE via the transceiver, a Radio ResourceControl (RRC) message including a second S-NSSAI list that includes oneor more S-NSSAIs, and transmit, to the UE via the transceiver, an RRCRelease message including a wait timer that limits further RRCconnection request by the UE until the wait timer expires, in a casewhere the one or more S-NSSAIs in the second S-NSSAI list only includethe one or more S-NSSAIs in the first S-NSSAI list.

A User Equipment (UE) according to a second exemplary aspect of thepresent disclosure includes a transceiver configured to communicate witha Next Generation Radio Access Network (NG-RAN) node, a processorconfigured to transmit, to the NG-RAN node via the transceiver, a RadioResource Control (RRC) message including a S-NSSAI list that includesone or more S-NSSAIs, and receive, from the NG-RAN node via thetransceiver, an RRC Release message including a wait timer that limitsfurther RRC connection establishment request by the UE until the waittimer expires, in a case where the one or more S-NSSAIs in the secondS-NSSAI list only indicate one or more congested network slicesrespectively, wherein the UE, does not initiate the further RRCconnection request until the wait timer expires.

A method for a Next Generation Radio Access Network (NG-RAN) nodeaccording to a third exemplary aspect of the present disclosure includesreceiving, from an Access-mobility Management Function (AMF) via an NGinterface between the NG-RAN node and the AMF, NGAP OVERLOAD STARTmessage including a first Single Network Slicing Selection AssistanceInformation (S-NSSAI) list that includes one or more S-NSSAIs indicatingone or more congested network slices respectively, receiving, from aUser Equipment (UE) via a transceiver implemented in the NG-RAN node, aRadio Resource Control (RRC) message including a second S-NSSAI listthat includes one or more S-NSSAIs, and transmitting, to the UE via thetransceiver, an RRC Release message including a wait timer that limitsfurther RRC connection request by the UE until the wait timer expires,in a case where the one or more S-NSSAIs in the second S-NSSAI list onlyinclude the one or more S-NSSAIs in the first S-NSSAI list.

A determination method used in an UE according to a Fourth exemplaryaspect of the present disclosure includes receiving an AN messagecontaining a list of S-NSSAI and wait time of each S-NSSAI in the listand determining that congestion related to network slice is occurredbased on the AN message.

A method for a User Equipment (UE) according to a Fourth exemplaryaspect of the present disclosure includes transmitting, to a NextGeneration Radio Access Network (NG-RAN) node via a transceiverimplemented in the UE, a Radio Resource Control (RRC) message includinga S-NSSAI list that includes one or more S-NSSAIs, and receiving, fromthe NG-RAN node via the transceiver, an RRC Release message including await timer that limits thither RRC connection request by the UE untilthe wait timer expires, in a case where the one or more S-NSSAIs in thesecond S-NSSAI list only indicate one or more congested network slicesrespectively, wherein the UE does not initiate the further RRCconnection request until the wait timer expires.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a procedure related to handling of congestion control at (R)ANnode and the UE.

FIG. 2 is a procedure for the scenario when the UE has NAS signalingconnection established and has at least one PDU session established.

FIG. 3 is a procedure related to release of network resources of acongested network slice(s) only and keeping network resources ofnon-congested slice(s).

FIG. 4 is a procedure releasing network resources related to all S-NSSAIif one S-NSSAI related to the UE is indicated as congested by the AMF.

FIG. 5 is a Handling of network slice related congestion at AN nodeduring service request procedure.

FIG. 6 is a procedure to handle congestion control by N3IWF.

FIG. 7 is a block diagram illustrating the main components of the UE.

FIG. 8 is a block diagram illustrating the main components of anexemplary (R)AN node.

FIG. 9 is a block diagram illustrating the main components of the AMF.

FIG. 10 is 5G System Architecture.

DESCRIPTION OF EMBODIMENTS

For the purposes of the present document, the abbreviations given in TR21.905 and the following apply. An abbreviation defined in the presentdocument takes precedence over the definition of the same abbreviation,if any, in TR 21.905,

-   5GC 5G Core Network-   5GS 5G System-   5G-AN 5G Access Network-   5G-GUTI 5G Globally Unique Temporary Identifier-   5G-S-I 5G S-Temporary Mobile Subscription Identifier-   5QI 5G QoS Identifier-   AF Application Function-   AMF Access and Mobility Management Function-   AN Access Node-   AS Access Stratum-   AUSF Authentication Server Function-   CP Control Plane-   DL Downlink-   DN Data Network-   DNAI DN Access Identifier-   DNN Data Network Name-   EDT Early Data Transmission-   FQDN Fully Qualified Domain Name-   GFBR Guaranteed Flow Bit Rate-   GMLC Gateway Mobile Location Centre-   GPSI Generic Public Subscription Identifier-   GUAMI Globally Unique AMF identifier-   HR Home Routed (roaming)-   LADN Local Area Data Network-   LBO Local Break Out (roaming)-   LMF Location Management Function-   LRF Location Retrieval Function-   MAC Medium Access Control-   MFBR Maximum Flow Bit Rate-   MICO Mobile initiated Connection Only-   N3IWF Non-3GPP Inter Working Function-   NAI Network Access Identifier-   NAS Non-Access Stratum-   NEF Network Exposure Function-   NF Network Function-   NG-RAN Next Generation Radio Access Network-   NR New Radio-   NRF Network Repository Function-   NSI ID Network Slice Instance Identifier-   NSSAI Network Slice Selection Assistance Information-   NSSF Network Slice Selection Function-   NSSP Network Slice Selection Policy-   PCF Policy Control Function-   PEI Permanent Equipment identifier-   PER Packet Error Rate-   PFD Packet Flow Description-   PPD Paging Policy Differentiation-   PPI Paging Policy Indicator-   PSA PDU Session Anchor-   QFI QoS Flow Identifier-   QoE Quality of Experience-   (R)AN (Radio) Access Network-   RLC Radio Link Control-   RQA Reflective QoS Attribute-   RQI Reflective QoS Indication-   RRC Radio Resource Control-   SA NR Standalone New Radio-   SBA Service Based Architecture-   SBI Service Based Interface-   SD Slice Differentiator-   SDAP Service Data Adaptation Protocol-   SEAF Security Anchor Functionality-   SEPP Security Edge Protection Proxy-   SMF Session Management Function-   S-NSSAI Single Network Slice Selection Assistance Information-   SSC Session and Service Continuity-   SST Slice/Service Type-   SUCI Subscription Concealed Identifier-   SUPI Subscription Permanent Identifier-   UDSF Unstructured Data Storage Function-   UL Uplink-   UL CL Uplink Classifier-   UPF User Plane Function-   UDR Unified Data Repository-   URSP UE Route Selection Policy

In order to make both general NAS level congestion control and networkslice congestion control works together, a procedure is needed by a(R)AN node to send a congested S-NSSAI with wait time to the UE so thatthe UE does not need initiates any signaling related to the S-NSSAI forthe duration of wait time due to following reasons:

(1) S-NSSAI and back off timer transmission by NAS message causesadditional load to AMF that is already in overload state, because theAMF needs to transmit the NAS message to large numbers of UEs.

(2) Number of the AN connected with one AMF is smaller than number ofthe UE which has connection with the one AMF.

(3) Therefore, by using AN message (from AN to UE) for S-NSSAI and backoff timer transmission, AMF has only to transmit the Overload message toAN.

The reasons also include to protect the (R)AN node when it is congestedor to prevent RAN node getting congested.

This invention discloses the following technical aspects to the overloadcontrol in the 5GS.

(1) A RAN node receives a N2 message (e.g. NGAP OVERLOAD START)containing a list of S-NSSAI of the congested network slice andoptionally a wait timer for each S-NSSAI in the list from AMF.

(2) The RAN node sends a list of S-NSSAI and a wait timer for eachS-NSSAI in the list in an AN signaling message to the UE when the RANreceives, from the UE, a AN signaling message containing a list ofS-NSSAI to establish AN signaling connection and the S-NSSAI(s) isindicated in the N2 message as congested by the AMF.

(3) Upon receiving the AN message containing a list of S-NSSAI and waittime of each S-NSSAI in the list by the UE, the UE determines(considers) that congestion related to network slice is occurred. Andthen, the UE does not initiate any NAS and AS procedure (i.e. does notsend any NAS or AS message) related to S-NSSAI contained in the list forthe timer period indicated in the wait time of an S-NSSAI, i.e. untilthe wait timer expires. In other words, the UE may initiate any NAS andAS procedure (i.e. sends some NAS or AS message) related to S-NSSAIcontained in the list if the wait timer expires.

(4) Upon receiving the AN message containing only wait time, the UEdetermines that the wait time is related to a NAS congestion or someother abnormal network conditions. The UE does not initiate any NAS andAS procedure for the period of wait time, i.e. until the wait timerexpires. The AN massage may contain an explicit indication that NAScongestion gets underway.

(5) In one scenario, the list of S-NSSAI contains a single S-NSSAI.

(6) In one scenario, the AN message to the UE contains an informationelement (e.g. AN cause, RRC cause) indicating congestion in the networktogether with list of S-NSSAI and wait time in the network. When the UEreceives the information element indicating congestion in the networkand together with a list of S-NSSAI and a wait time for each S-NSSAI inthe list, the UE determines (considers) that the network slicecorresponding to S-NSSAI in the list is congested. The UE does not sendany NAS or AS message related to the S-NSSAI present in the list tillthe period of wait time of the S-NSSAI expires. The list of S-NSSAI maybe composed of only configured S-NSSAI to the UE. The list of S-NSSAImay be composed of all S-NSSAI that the AMF is aware of them ascongested.

(7) In one scenario, the AN message to the UE contains an informationelement indicating network slice congestion together with list ofS-NSSAI and wait time for each S-NSSAI in the list. When the UE receivesthe AN message containing an information element indicating networkslice congestion then the UE determines (considers) that there iscongestion in the network slices corresponding to the S-NSSAI(s) presentin the list of S-NSSAI. The UE does not initiate any NAS procedure i.e.does not send any NAS or AS message related to S-NSSAI(s) present in thereceived S-NSSAI list till the time period of the wait timecorresponding to each S-NSSAI expires.

(8) In one scenario, the AN message to the UE does not contain any listof S-NSSAI but contains the information element (e.g. AN cause, RRCcause) indicating congestion in the network, then the UE determines(considers) that there is NAS level congestion in the network or ASlevel congestion in the network and does not initiate any NAS procedurei.e. does not send any NAS or AS message.

(9) The NAS procedure is Registration Management procedure (Registrationprocedure related to initial registration or mobility registration),Connection management (Service Request procedure) procedure and sessionmanagement procedure (PDU Session establishment or PDU sessionmanagement procedure). The AS procedure is AN signaling connectionestablishment procedure (e.g. RRC Connection Establishment procedure).

The FIG. 1 shows a procedure related to handling of congestion controlat (R)AN node and the UE when AMF indicates that congestion related tonetwork slice congestion or general NAS congestion.

The network ((R)AN and AMF) and the UE will follow the procedure asdescribed in the FIG. 1 and procedure as described below.

0. If AMF determines there is congestion in the network slice(s) the AMFsends a N2 message (NGAP OVERLOAD START) containing a list of S-NSSAIwhich are congested and optionally, the wait time for each S-NSSAI. Thevalue of the wait time is determined by the local congestion situationsin the AMF related to the network slices. If the AMF detects general NASlevel congestion then the network indicates it to the (R)AN node andoptionally contains wait time which value is determined by the AMFdepending on the network condition in the AMF.

1. The (R)AN node receives a N2 message(S-NSSAI(s), wait time(Optional)) (e.g. NGAP OVERLOAD START) containing a list of S-NSSAI ofthe congested network slice and optionally a wait timer for each S-NSSAIin the list from AMF. The N2 message is requesting the (R)AN node tostart overload control related to the list of S-NSSAI sent in theN2-message as per the procedure defined in sub clause 5.19.5.2 ofNon-patent literature 1 (TS 23.501). The wait time included for eachS-NSSAI indicates the period after which the network may not experiencenetwork slice related congestion. In other words, expiry of the waittimer may indicates it is expected that the network slice relatedcongestion was no longer.

2. The (R)AN node receives a first AN signaling message containing alist of S-NSSAI to establish a AN signaling connection from a UE. Thefirst AN signaling message is a RRC Connection Request message or a RRCConnection Setup complete message or any other existing RRC message or anew RRC message which is sent by the UE during the (R)AN signalingconnection establishment procedure. If the EDT procedure is enabled, alist of S-NSSAI may be sent by the UE using the RRC Connection Requestmessage.

3. The (R)AN node checks if S-NSSAI(s) received from the UE in step 2 iscontained in the S-NSSAI list received from the AMF in step 0. If any ofthe S-NSSAI of the UE S-NSSA list is contained in the AMF S-NSSAI listthen the (R)AN sends a second AN signaling message containing list ofmatching S-NSSAI and corresponding wait time to the UE as mentioned instep 4. The second AN signaling message is a RRC Connection Rejectmessage or RRC Connection Release message or any other existing RRCmessage or a new RRC message which is sent by the UE during the (R)ANsignaling connection establishment procedure to handle error cases when(R)AN connection cannot be established. The (R)AN node sends RRCConnection Reject if the first AN message is RRC Connection Requestmessage or the (R)AN sends RRC Connection Release message if the firstAN message is RRC connection setup complete message.

In one scenario in above case of step 3, the (R)AN node provides anadditional information in a first information element (e.g. AN cause orRRC cause) indicating the reason for failure in establishing the ANsignaling connection together with list of S-NSSAI and wait time in thesecond AN signaling message. The information element contains a valuecongestion if RAN detects general NAS level congestion or network slicecongestion if RAN detects congestion in the network slice(s).

In case, the AN signaling connection establishment is rejected due toNAS level congestion then the AN node set the information element withvalue congestion and includes wait time in the first AN message and doesnot include list of S-NSSAI and their wait time. In one case it justincludes wait time in the second AN signaling connection and does notinclude list of S-NSSAI and their wait time and the first informationelement.

In one scenario in the above case, the wait time sent for each S-NSSAIto the UE may be same as or based on the wait time provided by the AMFfor this S-NSSAI.

In one scenario in the above case, the wait time sent for each S-NSSAIto the UE is derived by the (R)AN node by considering the wait timereceived from the AN node for this S-NSSAI as one input parameter inderiving the wait time.

In one scenario when the wait time is not received from the AMF then the(R)AN decides wait time tor each S-NSSAI by itself or on some otherparameters provided by AMF in the N2 message.

4. The UE receives the second AN signaling message (e.g. RRC ConnectionReject). The UE releases the AN signaling connection if the AN signalingconnection was established or abort the AN signaling connection when ANsignaling connection establishment was initiated.

5. The UE optionally sends the third AN signaling message (e.g. RRCconnection Release complete if the second AN signaling message was RRCConnection Release Request). The third AN signaling message indicatesacknowledgment for the second AN signaling message and indicates thesuccessful release of the AN signaling connection when the AN connectionwas established successfully.

6. If the second AN signaling message contains the information elementset to network slice congestion or congestion, and contains the list ofS-NSSAI and wait time for each S-NSSAI then the UE does not initiate anyNAS or AS procedure related to the S-NSSAI present in the list for theperiod of corresponding wait time i.e. the UE does not send any NAS orAS signaling related to the S-NSSAI present in the S-NSSAI present inthe list for the period of corresponding wait time. The UE initiates NASprocedure or AS procedure related to a S-NSSAI not present in the listof S-NSSAI received from the (R)AN node i.e. the UE sends NAS or ASmessage related to a S-NSSAI not present in the list of S-NSSAI receivedfrom the (R)AN node.

If the second AN signaling message contains the list of S-NSSAI and waittime for each S-NSSAI and does not contain the first information elementthen the UE does not initiate any NAS or AS procedure related to theS-NSSAI present in the list for the period of corresponding wait timei.e. the UE does not send any NAS or AS signaling related to the S-NSSAIpresent in the S-NSSAI present in the list for the period ofcorresponding wait time. The UE initiates NAS procedure or AS procedurerelated to a S-NSSAI not present in the list of S-NSSAI received fromthe (R)AN node i.e. the UE sends NAS or AS message related to a S-NSSAInot present in the list of S-NSSAI received from the (R)AN node. The UEmay initiate NAS procedure or AS procedure related to a S-NSSAI presentin the list of S-NSSAI received from the (R)AN node if the wait timerexpires.

If the second AN signaling message contains wait time and does notcontain the list of S-NSSAI and their wait time, and the firstinformation element, then the UE does not initiates any NAS or ASprocedure i.e. the UE does not send any AS or NAS signaling message tothe network. The UE does not establish any AS or NAS signalingconnection. The UE determines that the AN signaling connectionestablishment fails due to general NAS level congestion.

If the second AN signaling message contains the information elementwhich value is set to congestion, and wait time but does not containlist of S-NSSAI and then the UE does not initiates any NAS or ASprocedure i.e. the UE does not send any AS or NAS signaling message tothenetwork. The UE does not establish any AS or NAS signalingconnection. The UE determines that the AN signaling connectionestablishment fails due to general NAS level congestion with thenetwork.

In another scenario, the AN, the UE and the AMF may performs asfollowing steps:

1. The AMF sends the N2 message indicating that overload is(full/partial) recovering in the AMF (e.g. OVERLOAD STOP message) to ANor triggers overload start procedure with new percentage value thatpermit more signalling traffic to be carried.

2. The AN transmits, to the UE, information indicating that theAMF/Slice is recovering, in response to the step 1. The informationindicating that the AMF/Slice is recovering may be broadcasted by theAN.

3. Upon reception of the information indicating that the AMF/Slice isrecovering, the UE may operate step (a) or (b) as following:

a. initiate the AN signaling connection upon reception of theinformation indicating that the AMF/Slice is recovering, even if theWait Time (back off timer) is running, or

b. consider that the Wait Time (wait timer) expires if the UE receivesthe information indicating that the AMF/Slice is recovering.

In this embodiment, the AMF determines the timer value and the AMFoptionally sends the timer value to the (R)AN node. However, the (R)ANnode can determine the timer value instead of the AMF. The (R)AN nodecan determine the timer value based on information from the AMF. Theinformation can be, for example, load level information (e.g. 1. veryhigh/high/middle/low 2. percentage of the load). The variation that the(R)AN node determines the timer value can be applied to other embodimentin this description.

The FIG. 2 shows a procedure for the scenario when the UE has NASsignaling connection established and has at least one PDU sessionestablished.

The network ((R)AN and AMF) and the UE will follow the procedure asdescribed in the FIG. 2 and procedure as described below.

0. A UE has established PDU sessions related to different network slices(i.e. different S-NSSAI).

1. The AN receives a N2 message (e.g NGAP OVERLOAD START) containing alist of congested S-NSSAI from the AMF.

2. The AN identifies that not all S-NSSAI of the UE is congested.

3. The AN initiates a selective release of the network resources relatedto the congested S-NSSAI(s) by sending a first AN signaling messagecontaining a list of congested S-NSSAI and instructing the UE to releasethe network resources. The AN sends, to the UE, the first AN signalingmessage. This first AN message is a new AN message or existing ANmessage containing a new information element indicating to release thenetwork resources related to S-NSSAI.

4. The UE sends the second AN signaling message to the AN indicating anacknowledgement of the first AN signaling message.

5. When a UE receives a first AN signaling message from the ANcontaining list of S-NSSAI and indicating the UE to release the networkresources then the UE will release all the network resources related tothe S-NSSAI present in the list but keep the PDU session(s) established.The network resources are AN resources and CN resources. The AN and CNresources further comprise signalling (i.e. control plane) resources anduser plane resources. The example of AN resources are DRB and SRB andexample of the CN resources are GTF-U resources and QoS flows. Fromanother perspective, the AN resources may be all radio resourcesincluding at least one of the RLC entity, the MAC configuration and theassociated PDCP entity for all established radio bearers.

In the description above, AN signaling message is shown. An example ofthe AN signaling message is RRC connection release.

Also, in the description above, an example to release the networkresources relates to S-NSSAI. The network resource can be identified bynot only the S-NSSAI but also a current PDU session ID.

When the UE sends, to the AMF, a PDU session Establish Request whichincludes any one of parameters below after a back-off timer expires.

-   -   S-NSSAI    -   Current(or Old) PDU session ID    -   New PDU session ID    -   Combination of the parameters above

This resource identification in this embodiment can be applied to otherembodiment in this description.

The FIG. 3 shows a procedure related to release of network resources ofa congested network slice(s) only and keeping network resources ofnon-congested slice(s).

In this procedure the network resources are AN resources and CNresources. The AN and CN resources further comprise signalling resourcesand user plane resources. The example of AN resources is DRB and SRB andexample of the CN resources are GTP-U resources and QoS flows. Fromanother perspective, the AN resources may be all radio resourcesincluding at least one of the RLC entity, the MAC configuration and theassociated PDCP entity for all established radio bearers.

0. The UE has NAS signalling connection established and has PDU sessionsestablished for more than one S-NSSAI.

1. The (R)AN node receives a N2 message(S-NSSAI(s), wait time(Optional)) (e.g. NGAP OVERLOAD START) containing a list of S-NSSAI ofthe congested network slice and optionally a wait timer for each S-NSSAIin the list from AMF. The N2 message is requesting the (R)AN node tostart overload control related to the list of S-NSSAI sent in theN2-message as per the procedure defined in sub clause 5.19.5.2 of Nonpatent literature 1. The wait time included for each S-NSSAI indicatesthe period after which the network may not experience network slicerelated congestion.

2. If a UE has PDU sessions established for the S-NSSAI(s) indicated inthe first N2 message and the UE has PDU session(s) for the S-NSSAI notindicated in the S-NSSAI then the (R)AN node sends a first AN signalingmessage containing a list of S-NSSAI and wait timer for each S-NSSAI inthe list and requests a UE to release the network resources related tothe S-NSSAI indicated in the list and keep the PDU session(s)established. The (R)AN node keeps the network resources for the PDUsessions related to S-NSSAI(s) not indicated in the first N2 message.The first AN signaling message is a new message or an existing ANsignaling message.

3. A UE receives the first AN signaling message containing a list ofS-NSSAI and corresponding wait time. The UE releases all the networkresources related to the indicated S-NSSAI(s) and keep the PDUsession(s) established. The UE does not release any network resourcesrelated to the S-NSSAI which not indicated in the first AN signalingmessage.

4. The UE sends the second AN signaling message to the AN.

5. If the first AN signaling message contains the information elementset to network slice congestion or congestion, and contains the list ofS-NSSAI and wait time for each S-NSSAI then the UE does not initiate anyNAS or AS procedure related to the S-NSSAI present in the list for theperiod of corresponding wait time i.e. the UE does not send any NAS orAS signaling related to the S-NSSAI present in the S-NSSAI present inthe list for the period of corresponding wait time. The UE initiates NASprocedure or AS procedure related to a S-NSSAI not present in the listof S-NSSAI received from the (R)AN node i.e. the UE sends NAS or ASmessage related to a S-NSSAI not present in the list of S-NSSAI receivedfrom the (R)AN node.

If the first AN signaling message contains the list of S-NSSAI and waittime for each S-NSSAI and does not contain the first information elementthen the UE does not initiate any NAS or AS procedure related to theS-NSSAI present in the list for the period of corresponding wait timei.e. the UE does not send any NAS or AS signaling related to the S-NSSAIpresent in the S-NSSAI present in the list for the period ofcorresponding wait time. The UE initiates NAS procedure or AS procedurerelated to a S-NSSAI not present in the list of S-NSSAI received fromthe (R)AN node i.e. the UE sends NAS or AS message related to a S-NSSAInot present in the list of S-NSSAI received from the (R)AN node.

6. After step 2, the (R)AN node sends a second N2 message to the AMFcontaining list of S-NSSAI and UE ID requesting AMP to release thenetwork resources related to the PDU sessions established for theS-NSSAI(s) present in the list. The N2 message is a new N2 message.

The AMP receives the second N2 message and initiates network resourcesrelease procedure related to the PDU session(s) corresponding to theS-NSSAI(s) present in the list by sending a message to the related SMF.

7. The SMF on receiving the N11 message releases the network resourcesrelated to the PDU session(s) which are related to S-NSSAI(s) of the UE.The SMF optionally sends a response message back to AMP indicating thesuccessful release of the network resources related to PDU session(s) ofindicated S-NSSAI(s).

8. The AMF receives a second N11 message. The AMF optionally sends athird N2 message acknowledging the successful release of the networkresources related to the PDU session(s) of indicated S-NSSAI(s).

9. The (R)AN on receiving the third N2 message completes the networkresource release procedure for the UE.

The FIG. 4 shows a procedure releasing network resources related to allS-NSSAI if one S-NSSAI related to the UE is indicated as congested bythe AMF. This procedure discloses the following technical aspects to theoverload control in the 5GS.

(1) A UE has established PDU session(s) for different network slices.The AN receives a N2 message containing a list of congested S-NSSAI. TheAN identifies that not all S-NSSAI of the UE is indicated as congestedand initiates a release all the network resources of the UE by sending aAN signaling message. The AN message is an existing AN messageindicating release of all network resources or a new AN messagerequesting the UE to release all the network resources.

(2) When a UE receives a AN messaging which requests to release all thenetwork resources then the UE will release all the network resourcesallocated to the UE. The UE goes to idle state.

0. The UE has NAS signalling connection established and has PDU sessionsestablished for more than one S-NSSAI.

1. The (R)AN node receives a N2 message(S-NSSAI(s), wait time(Optional)) (e.g. NGAP OVERLOAD START) containing a list of S-NSSAI ofthe congested network slice and optionally a wait timer for each S-NSSAIin the list from AMF. The N2 message is requesting the (R)AN node tostart overload control related to the list of S-NSSAI sent in theN2-message as per the procedure defined in sub clause 5.19.5.2 of Nonpatent literature 1. The wait time included for each S-NSSAI indicatesthe period after which the network may not experience network slicerelated congestion.

2. RAN checks for a UE if the UE has PDU sessions established for theS-NSSAI(s) which is indicated in the first N2 message and the UE hasPDI) sessions for the S-NSSAI which is not indicated in the S-NSSAI thenthe (R)AN node initiates release of network resources by sending a firstAN message containing list of S-NSSAI of the UE which was indicated bythe AMF, corresponding wait time and optionally a First InformationElement indicating cause of release of AN connection.

In one scenario in above case of step 2, the (R)AN node provides anadditional information in a first information element (e.g. AN cause orRRC cause) indicating the reason for failure in establishing the ANsignaling connection together with list of S-NSSAI and wait time in thesecond AN signaling message. The information element contains a valuecongestion if RAN detects general NAS level congestion or network slicecongestion if RAN detects congestion in the network slice(s).

In case the AN signaling connection establishment is rejected due to NASlevel congestion then the AN node set the information element with valuecongestion and includes wait time in the first AN message and does notinclude list of S-NSSAI and their wait time. In one case it justincludes wait time in the second AN signaling connection and does notinclude list of S-NSSAI and their wait time and the first informationelement.

In one scenario in the above case the wait time sent for each S-NSSAI tothe UE is same as the wait time provided by the AMF for this S-NSSAI.

In one scenario in the above case the wait time sent for each S-NSSAI tothe UE is derived by the (R)AN node by considering the wait timereceived from the AN node for this S-NSSAI as one input parameter inderiving the wait time.

In one scenario when the wait time is not received from the AMF then the(R)AN decides wait time for each S-NSSAI by itself or on some otherparameters provided by AIF in the N2 message.

3. The UE receives the second AN signaling message. The UE releases theAN signaling connection if the AN signaling connection was establishedor abort the AN signaling connection when AN signaling connectionestablishment was initiated.

4. The UE optionally sends the third AN signaling message (e.g. RRCconnection Release complete if the second AN signaling message was RRCConnection Release Request) acknowledging the second AN signalingmessage and indicating the successful release of the AN signalingconnection when the AN connection was established successfully.

5. If the second AN signaling message contains the information elementset to network slice congestion or congestion, and contains the list ofS-NSSAI and wait time for each S-NSSAI then the UE does not initiate anyNAS or AS procedure related to the S-NSSAI present in the list for theperiod of corresponding wait time i.e. the UE does not send any NAS orAS signaling related to the S-NSSAI present in the S-NSSAI present inthe list for the period of corresponding wait time. The UE initiates NASprocedure or AS procedure related to a S-NSSAI not present in the listof S-NSSAI received from the (R)AN node i.e. the UE sends NAS or ASmessage related to a S-NSSAI not present in the list of S-NSSAI receivedfrom the (R)AN node.

If the second AN signaling message contains the list of S-NSSAI and waittime for each S-NSSAI and does not contain the first information elementthen the UE does not initiate any NAS or AS procedure related to theS-NSSAI present in the list for the period of corresponding wait timei.e. the UE does not send any NAS or AS signaling related to the S-NSSAIpresent in the S-NSSAI present in the list for the period ofcorresponding wait time. The UE initiates NAS procedure or AS procedurerelated to a S-NSSAI not present in the list of S-NSSAI received fromthe (R)AN node i.e. the UE sends NAS or AS message related to a S-NSSAInot present in the list of S-NSSAI received from the (R)AN node.

If the second AN signaling message contains wait time and does notcontain the list of S-NSSAI and their wait time, and the firstInformation element, then the UE does not initiates any NAS or ASprocedure i.e. the UE does not send any AS or NAS signaling message tothe network. The UE does not establish any AS or NAS signalingconnection.

If the second AN signaling message contains the information elementwhich value is set to congestion, and wait time but does not containlist of S-NSSAI and then the UE does not initiates any NAS or ASprocedure i.e. the UE does not send any AS or NAS signaling message tothe network. The UE does not establish any AS or NAS signalingconnection.

6. The (R)AN node initiate UE context release procedure as defined insub clause 4.2.6 of TS Non patent literature 1.

The FIG. 5 shows a handling of network slice related congestion at ANnode during service request procedure. This procedure discloses thefollowing technical aspects to the overload control in the 5GS.

(1) A UE includes a S-NSSAI related to the PDU session which is to beactivated in a AN signaling message during the AN signaling connectionestablishment. If the service request is to be triggered to activatemore than one PDU session and these PDU sessions is related to differentS-NSSAI then the UE includes all S-NSSAI in the AN signaling message.

(2) The RAN node rejects the AN signaling connection establishment whenit receives an AN signaling message containing a S-NSSAI or list ofS-NSSAIs for which the RAN has received a N2 message instructing the RANnode to reject a AN signaling connection establishment.

0. A LE is registered to a PLMN and is in idle state has no signalingconnection.

1. The (R)AN node receives a N2 message(S-NSSAI(s), wait time(Optional)) (e.g. NGAP OVERLOAD START) containing a list of S-NSSAI ofthe congested network slice and optionally a wait timer for each S-NSSAIin the list from AMF. The N2 message is requesting the (R)AN node tostart overload control related to the list of S-NSSAI sent in theN2-message as per the procedure defined in sub clause 5.19.5.2 of Nonpatent literature 1. The wait time included for each S-NSSAI indicatesthe period after which the network may not experience network slicerelated congestion.

2. The UE gets trigger to initiate service request procedure. Forexample due to trigger to establish a PDU session or trigger to initiateuser plane connection for an established PDU session.

3. The UE initiates AN Signaling connection establishment procedure andsends a first AN signaling message containing S-NSSAI of the PDU sessionto be established. The first AN signaling connection is a first ANsignaling message (RRC Connection Request message) sent by the UE to the(R)AN during AN Signaling connection establishment procedure or a secondAN signaling message (RRC Connection setup complete) sent by a UE to(R)AN node after the UE receives a AN signaling message from the (R)ANin response of first AN message of the UE during AN signaling connectionestablishment.

4. The RAN node receives the first AN signaling connection Requestmessage containing S-NSSAI and establishment cause. The (R)AN noderejects AN signalling connection establishment procedure when a S-NSSAIpresent in the AN signalling message is indicated in the first N2signalling message as congested. The (R)AN node sends a second ANsignalling message containing (S-NSSAI and wait tine, AN cause(optional)).

In one scenario in above case of step 4, the (R)AN node provides anadditional information in a first information element (e.g. AN cause orRRC cause) indicating the reason for failure in establishing the ANsignaling connection together with list of S-NSSAI and wait time in thesecond AN signaling message. The information element contains a valuecongestion if RAN detects general NAS level congestion or network slicecongestion if RAN detects congestion in the network slice(s).

In case the AN signaling connection establishment is rejected due to NASlevel congestion then the AN node set the information element with valuecongestion and includes wait time in the first AN message and does notinclude list of S-NSSAI and their wait time. In one case it justincludes wait time in the second AN signaling connection and does notinclude list of S-NSSAI and their wait time and the first informationelement.

In one scenario in the above case the wait time sent fbr each S-NSSAI tothe UE is same as the wait time provided by the AMF for this S-NSSAI.

In one scenario in the above case the wait time sent fbr each S-NSSAI tothe UE is derived by the (R)AN node by considering the wait timereceived from the AN node for this S-NSSAI as one input parameter inderiving the wait time.

In one scenario when the wait time is not received from the AMF then the(R)AN decides wait time for each S-NSSAI by itself or on some otherparameters provided by AMF in the N2 message.

5. The UE receives the second AN signaling message. The UE releases theAN signaling connection if the AN signaling connection was establishedor abort the AN signaling connection when AN signaling connectionestablishment was initiated.

6. The UE optionally sends the third AN signaling message (e.g. RRCconnection Release complete if the second AN signaling message was RRCConnection Release Request) acknowledging the second AN signalingmessage and indicating the successful release of the AN signalingconnection when the AN connection was established successfully.

7. If the second AN signaling message contains the information elementset to network slice congestion or congestion, and contains the list ofS-NSSAI and wait time for each S-NSSAI then the UE does not initiate anyNAS or AS procedure related to the S-NSSAI present in the list for theperiod of corresponding wait time i.e. the UE does not send any NAS orAS signaling related to the S-NSSAI present in the S-NSSAI present inthe list for the period of corresponding wait time. The UE initiates NASprocedure or AS procedure related to a S-NSSAI not present in the listof S-NSSAI received from the (R)AN node i.e. the UE sends NAS or ASmessage related to a S-NSSAI not present in the list of S-NSSAI receivedfrom the (R)AN node.

If the second AN signaling message contains the list of S-NSSAI and waittime for each S-NSSAI and does not contain the first information elementthen the UE does not initiate any NAS or AS procedure related to theS-NSSAI present in the list for the period of corresponding wait timei.e. the UE does not send any NAS or AS signaling related to the S-NSSAIpresent in the S-NSSAI present in the list for the period ofcorresponding wait time. The UE initiates NAS procedure or AS procedurerelated to a S-NSSAI not present in the list of S-NSSAI received fromthe (R)AN node i.e. the UE sends NAS or AS message related to a S-NSSAInot present in the list of S-NSSAI received from the (R)AN node.

If the second AN signaling message contains wait time and does notcontain the list of S-NSSAI and their wait time, and the firstInformation element, then the UE does not initiates any NAS or ASprocedure i.e. the UE does not send any AS or NAS signaling message tothe network. The UE does not establish any AS or NAS signalingconnection.

If the second AN signaling message contains the information elementwhich value is set to congestion, and wait time but does not containlist of S-NSSAI and then the UE does not initiates any NAS or ASprocedure i.e. the UE does not send any AS or NAS signaling message tothe network. The UE does not establish any AS or NAS signalingconnection.

The FIG. 6 shows a procedure to handle congestion control by N3IWF. Thisprocedure discloses the following technical aspects to the overloadcontrol in the 5GS.

(1) When a N3IWF receives EAP message for 5G and containing a list ofS-NSSAI and the N3IWF has received a N2 message (e.g. NGAP OVERLOADSTART) to reject the AN connection establishment for the S-NSSAI presentin the list of S-NSSAI then the N3IWF sends an EAP message for 5Gcontaining the list of S-NSSAI and wait time for each S-NSSAI present inthe S-NSSAI list. When the N3IWF receives a N2 message (e.g. NGAPOVERLOAD START) indicating NAS level congestion control then the N3IWFrejects the AN signaling connection establishment procedure and send await time.

(2) When a UE receives a wait time in EAP response then the UE does notinitiate any NAS procedure i.e. does not send any NAS or AS messagerelated till the time period of the wait time. When a UE receives a listof S-NSSAI and wait time for each S-NSSAI in the EAP message then the UEdoes not initiate any NAS or AS procedure related to S-NSSAI present inthe list for the duration of wait time of the S-NSSAI.

0. The UE is in the idle.

1. Either step 1a or 1b takes place.

If an AMF detects NAS level congestion control then it sends N2 message(e.g NGAP OVERLOAD START message) containing (wait time) requesting theN3IWF to perform overload control as per the sub clause 5.19.5.2 of Nonpatent literature 1. If the AMF detects slice related network congestionthen it will send an N2 message containing a list of S-NSSAI of thenetwork slices which are congested and requesting the LE to perform ANoverload control as per the sub clause 5.19.5.2 of Non patentliterature 1. The network also includes wait time for each S-NSSAI inthe list.

2. The UE is in the idle.

3. The UE initiates NAS procedure (Registration procedure related toinitial attach or mobility, or Service Request procedure). The UEexecutes steps 1 to 5 are executed as defined in sub clause 4.12.2.2 ofTS 23.502 for registration procedure or service request procedure.

4. Either step 4a or 4b takes place.

The UE sends service request in IKE_AUTH_REQ message as mentioned instep 4b in the above figure and registration request in IKE_AUTH_REQmessage as mentioned in step 4a in the FIG. 6.

Step 4a may contains a parameter that indicates that this message is forthe attach request or registration request as the IKE parameter or asthe EAP parameter. Step 4b may contains a parameter that indicates thatthis message is for the service request as the IKE parameter or as theEAP parameter. Step 4b may contains an S-NSSAI parameter that indicatesthat an S-NSSAI that UE wishes to establish the PDU connection in theIKE parameter or in the EAP parameter.

5. Either step 5a or 5b takes place.

The N3IWF sends an IKE message containing a wait time and an optionalinformation element AN cause which is set to a value (e.g. congestion)related to NAS congestion when it receives a N2 message in step 1a toperform NAS level congestion controlor

The N3IWF sends an IKE message containing a list of S-NSSAI whichpresent in the step 4a or 4b and indicated as congested in the first N2message in step 1a. The IKE message also contains wait time for eachS-NSSAI in present in the list. The IKE message optionally contains aninformation element indicating network slice related congestion.

The message is step 5 is as defined as follows:

-   IKE_AUTH_RSP(EAP-RES/5G-NAS/[AN-PARAM (S-NSSAI(s) and wait time), AN    cause (optional))-   IKE_AUTH_RSP(EAP-REQ/5G-NAS/[AN-PARAM (S-NSSAI(s) and wait time), AN    cause (optional))-   IKE_AUTH_REQ(EAP-RES/5G-NAS/[AN-PARAM (S-NSSAI(s) and wait time), AN    cause (optional))-   IKE_AUTH_REQ(EAP-REQ/5G-NAS/[AN-PARAM (S-NSSAI(s) and wait time), AN    cause (optional))-   IKE AUTH_RSP(EAP-RES/5G-NAS/[AN-PARAM (wait time), AN cause    optional))-   IKE_AUTH_RSP(EAP-REQ/5G-NAS/[AN-PARAM (wait time), AN cause    (optional))-   IKE_AUTH_REQ(EAP-RES/5G-NAS/[AN-PARAM (wait time), AN cause    (optional))-   IKE_AUTH_REQ(EAP-REQ/5G-NAS/[AN-PARAM (wait time), AN cause    (optional))

6. Either step 6a or 6b takes place in accordance with step 5.

If the IKE message in step 5 contains the information element set tonetwork slice congestion or congestion, and contains the list of S-NSSAIand wait time for each S-NSSAI then the UE does not initiate any NAS orAS procedure related to the S-NSSAI present in the list for the periodof corresponding wait time i.e. the UE does not send any NAS or ASsignaling related to the S-NSSAI present in the S-NSSAI present in thelist for the period of corresponding wait time. The UE initiates NASprocedure or AS procedure related to a S-NSSAI not present in the listof S-NSSAI received from the (R)AN node i.e. the UE sends NAS or ASmessage related to a S-NSSAI not present in the list of S-NSSAI receivedfrom the (R)AN node.

If the IKE AN message is step 5 contains the list of S-NSSAI and waittime for each S-NSSAI and does not contain the first information elementthen the UE does not initiate any NAS or AS procedure related to theS-NSSAI present in the list for the period of corresponding wait timei.e. the UE does not send any NAS or AS signaling related to the S-NSSAIpresent in the S-NSSAI present in the list for the period ofcorresponding wait time. The UE initiates NAS procedure or AS procedurerelated to a S-NSSAI not present in the list of S-NSSAI received fromthe (R)AN node i.e. the UE sends NAS or AS message related to a S-NSSAInot present in the list of S-NSSAI received from the (R)AN node.

If the IKE message in step 5 contains wait time and does not contain thelist of S-NSSAI and their wait time, and the first Information element,then the UE does not initiates any NAS or AS procedure i.e. the UE doesnot send any AS or NAS signaling message to the network. The UE does notestablish any AS or NAS signaling connection.

If the IKE message in step 5 contains the information element whichvalue is set to congestion, and wait time hut does not contain list ofS-NSSAI and then the UE does not initiates any NAS or AS procedure i.e.the UE does not send any AS or NAS signaling message to the network. TheUE does not establish any AS or NAS signaling connection.

User Equipment (UE)

FIG. 7 is a block diagram illustrating the main components of the UE. Asshown, the UE (100) includes a transceiver circuit (103) which isoperable to transmit signals to and to receive signals from theconnected node(s) via one or more antenna (104). Although notnecessarily shown in FIG. 7, the UE will of course have all the usualfunctionality of a conventional mobile device (such as a user interface(102)) and this may be provided by any one or any combination ofhardware, software and firmware, as appropriate. Software may bepre-installed in the memory and/or may be downloaded via thetelecommunication network or from a removable data storage device (RMD),for example.

A controller (101) controls the operation of the UE in accordance withsoftware stored in a memory (105). The software includes, among otherthings, an operating system and a communications control module (106)having at least a transceiver control module (107). The communicationscontrol module (106) (using its transceiver control sub-module) isresponsible for handling (generating/sending/receiving) signalling anduplink/downlink data packets between the UE and other nodes, such as thebase station/(R)AN node, the AMF (and other core network nodes). Suchsignalling may include, for example, appropriately formatted signallingmessages relating to connection establishment and maintenance (e.g. RRCconnection establishment and other RRC messages), periodic locationupdate related messages (e.g. tracking area update, paging area updates,location area update, RAN notification area (RNA) update) etc.

(R)AN Node

FIG. 8 is a block diagram illustrating the main components of anexemplary (R)AN node (200), for example a base station (‘gNB’ in 5G). Asshown, the (R)AN node (200) includes a transceiver circuit (203) whichis operable to transmit signals to and to receive signals from connectedUE(s) via one or more antenna (204) and to transmit signals to and toreceive signals from other network nodes (either directly or indirectly)via a network interface (202). A controller (201) controls the operationof the (R)AN node in accordance with software stored in a memory (205).Software may be pre-installed in the memory and/or may be downloaded viathe telecommunication network or from a removable data storage device(RMD), for example. The software includes, among other things, anoperating system and a communications control module (206) having atleast a transceiver control module.

The communications control module (206) (using its transceiver controlsub-module) is responsible for handling (generating/sending/receiving)signalling between the (R)AN node and other nodes, such as the UE, theAMF, and the UDM/UDR (e.g. directly or indirectly). The signalling mayinclude, for example, appropriately formatted signalling messagesrelating to a radio connection and location procedures (for a particularUE), and in particular, relating to connection establishment andmaintenance (e.g. RRC connection establishment and other RRC messages),periodic location update related messages (e.g. tracking area update,paging area updates, location area update, RAN notification area (RNA)update), N2 messaging (e.g. to activate an N2 connection, to convey anNAS message from the UE, to provide any RRC Inactive state featurecapability support information to the AMF, and related N2request/response messages from the core network), etc.

The controller is also configured (by software or hardware) to handlerelated tasks such as, when implemented, RRC Inactive stateoptimisation, UE mobility estimate and/or moving trajectory estimation.

AMF

FIG. 9 is a block diagram illustrating the main components of the AMF(300). As shown, the AMF (300) includes a transceiver circuit (303)which is operable to transmit signals to and to receive signals fromother nodes (including the UE) via a network interface (302). Acontroller (301) controls the operation of the AMF (300) in accordancewith software stored in a memory (304). Software may be pre-installed inthe memory (304) and/or may be downloaded via the telecommunicationnetwork or from a removable data storage device (RMD), for example. Thesoftware includes, among other things, an operating system and acommunications control module (305) having at least a transceivercontrol module.

The communications control module (using its transceiver controlsub-module) is responsible for handling (generating/sending/receiving)signalling between the AMF and other nodes, such as the UE, basestation/(R)AN node, and UDM/UDR (directly or indirectly). Suchsignalling may include, for example, appropriately formatted signallingmessages relating to the procedures described herein, for example, N2messaging (e.g. from the (R)AN to activate an N2 connection, to conveyan NAS message from the UE, and to provide any RRC inactive statefeature capability support information to the AM, and related N2request/response messages to the (R)AN to provide, if implemented,(further) RRC inactive assistance information), signalling messagesrelating to UE subscription enquiries, etc.

Another Embodiment

AS (Access Stratum) may include an RRC layer, a SADP layer, a PDCPlayer, a RLC layer, a MAC layer and PHY layer.

NGRAN may include an eNB (evolved Node B) connected with 5GC and gNB,

The “wait time” as mentioned above may be denoted as “wait timer”.

The “AN signaling message” in downlink as mentioned above may be“RRCConnectionReject”, “RRCConnectionRelease” or“RRCConnectionReestablishmentReject”.

The “AN signaling message” in uplink as mentioned above may be“RRCConnectionRequest”, “RRCConnectionReestablishmentRequest”,“RRCConnectionResumeComplete”, “RRCConnectionResumeRequest” or“RRCConnectionSetupComplete”.

This application is based upon and claims the benefit of priority fromIndian patent applications No. 201811006021, filed on Feb. 16, 2018, thedisclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

-   100 UE-   101 controller-   102 user interface-   103 transceiver circuit-   104 antenna-   105 memory-   106 control module-   107 transceiver control module-   200 (R)AN node-   201 controller-   202 network interface-   203 transceiver circuit-   204 antenna-   205 memory-   206 communications control module-   207 transceiver control module-   300 AMF-   301 controller-   302 network interface-   303 transceiver circuit-   304 memory-   305 communications control module-   306 transceiver control module

1-10. (canceled)
 11. A Next Generation Radio Access Network (NG-RAN)node comprising: a receiver; and a transmitter, wherein the receiver isconfigured to receive, from an Access-mobility Management Function(AMF), an NGAP OVERLOAD START message, wherein the NGAP OVERLOAD STARTmessage includes one or more first Single Network Slicing SelectionAssistance Information (S-NSSAIs) identifying one or more overloadednetwork slices, wherein the receiver is configured to receive, from aUser Equipment (UE), a Radio Resource Control (RRC) message, wherein theRRC message includes a list of one or more second S-NSSAIs, wherein thetransmitter is configured to transmit, to the UE, an RRC Release messagein a case where the list only includes the one or more first S-NSSAIs,wherein the RRC Release message includes a value of a timer, and whereinthe timer limits further RRC connection request by the UE until thetimer expires.
 12. The NG-RAN node according to claim 11, wherein theRRC message is caused by a service request procedure.
 13. The NG-RANnode according to claim 11, wherein the one or more second S-NSSAIs arerelated to a PDU session to be activated.
 14. The NG-RAN node accordingto claim 11, wherein the value is associated with the one or more secondS-NSSAIs.
 15. The NG-RAN node according to claim 11, wherein the RRCmessage is an RRC Setup Complete message.
 16. A User Equipment (UE)comprising: a transmitter; a receiver; and a processor, wherein thetransmitter is configured to transmit, to a Next Generation Radio AccessNetwork (NG-RAN) node, a Radio Resource Control (RRC) message, whereinthe RRC message includes a list of one or more Single Network SlicingSelection Assistance Information (S-NSSAIs), wherein the receiver isconfigured to receive, from the NG-RAN node, an RRC Release message in acase where the list only includes one or more S-NSSAIs identifying oneor more overloaded network slices, wherein the RRC Release messageincludes a value of a timer, wherein the timer limits further RRCconnection request by the UE until the timer expires, and wherein theprocessor is configured to not initiate the further RRC connectionrequest until the timer expires.
 17. The UE according to claim 16,wherein the RRC message is caused by a service request procedure. 18.The UE according to claim 16, wherein the one or more S-NSSAIs includedin the list are related to a PDU session to be activated.
 19. The UEaccording to claim 16, wherein the value is associated with the one ormore S-NSSAIs included in the list.
 20. The UE according to claim 16,wherein the RRC message is an RRC Setup Complete message.
 21. A methodfor a Next Generation Radio Access Network (NG-RAN) node, the methodcomprising: receiving, from an Access-mobility Management Function(AMF), an NGAP OVERLOAD START message, wherein the NGAP OVERLOAD STARTmessage includes one or more first Single Network Slicing SelectionAssistance Information (S-NSSAIs) identifying one or more overloadednetwork slices; receiving, from a User Equipment (UE), a Radio ResourceControl (RRC) message, wherein the RRC message includes a list of one ormore second S-NSSAIs; and transmitting, to the UE, an RRC Releasemessage in a case where the list only includes the one or more firstS-NSSAIs, wherein the RRC Release message includes a value of a timer,and wherein the timer limits further RRC connection request by the UEuntil the timer expires.
 22. The method according to claim 21, whereinthe RRC message is caused by a service request procedure.
 23. The methodaccording to claim 21, wherein the one or more second S-NSSAIs arerelated to a PDU session to be activated.
 24. The method according toclaim 21, wherein the value is associated with the one or more secondS-NSSAIs.
 25. The method according to claim 21, wherein the RRC messageis an RRC Setup Complete message.
 26. A method for a User Equipment(UE), the method comprising: transmitting, to a Next Generation RadioAccess Network (NG-RAN) node, a Radio Resource Control (RRC) message,wherein the RRC message includes a list of one or more Single NetworkSlicing Selection Assistance Information (S-NSSAIs); and receiving, fromthe NG-RAN node, an RRC Release message in a case where the list onlyincludes one or more S-NSSAIs identifying one or more overloaded networkslices, wherein the RRC Release message includes a value of a timer,wherein the timer limits further RRC connection request by the UE untilthe timer expires, and wherein the UE is configured to not initiate thefurther RRC connection request until the timer expires.
 27. The methodaccording to claim 26, wherein the RRC message is caused by a servicerequest procedure.
 28. The method according to claim 26, wherein the oneor more S-NSSAIs included in the list are related to a PDU session to beactivated.
 29. The method according to claim 26, wherein the value isassociated with the one or more S-NSSAIs included in the list.
 30. Themethod according to claim 26, wherein the RRC message is an RRC SetupComplete message.